An FBI agent comforts a man whose loved one was still trapped in the rubble of the bombed Murrah Federal BuildingReuters

The 20th anniversary of the bombing of the Alfred Murrah Federal Building in Oklahoma City on 19 April 1995 marks the worst terrorist attack on US soil, prior to the 9/11 attacks in 2001. The blast was equivalent to 5,000 pounds (2,300kg) of TNT and killed 168 people, injured more than 600 and destroyed 324 nearby buildings, leaving many homeless.

Twenty years on, a memorial and museum stands on the site of the attack carried out by Timothy McVeigh and Terry Nichols. On the anniversary of the tragedy, we look at facts about the Oklahoma City bombing:

1) The truck filled with explosives was parked directly under the America's Kids Day Care Centre in the federal building. Of the 21 children there that morning, only six survived.

2) The blast measured around 3.0 on the Richter scale and could be heard up to 55 miles – or 89 km – away.

3) The victims, including three pregnant women, ranged in age from three months to 73 years – 99 of the victims worked for the government.

4) McVeigh graduated from the US Army Infantry School at Fort Benning, Georgia, in May 1988, where he had met Nichols. While training, McVeigh used much of his spare time to read about firearms, sniper tactics, and explosives.

5) McVeigh and Nichols purchased or stole the materials they needed to manufacture the bomb the year before the attack, which they stored in rented sheds until two days before.

6) Reports suggested McVeigh and Nichols burgled gun collector Roger E Moore in his home of $60,000 worth of guns, gold, silver and jewels, transporting the property in the victim's own van, but this is disputed.

The north side of the Alfred Murrah Federal Building in Oklahoma City after the bombingGetty

7) The damage caused by the blast was estimated to be worth $652m, destroying over 300 buildings, burning 86 cars and shattered glass in 258 buildings. Substantial donations were received from all over the United States.

8) The broken glass alone accounted for 5% of the death total and 69% of the injuries outside the Murrah Federal Building.

9) McVeigh was arrested within 90 minutes of the explosion. He was travelling north on Interstate 35 in Noble County, Oklahoma, and was stopped for driving a yellow 1977 Mercury Marquis with no number plate. When his car was searched, police found the words "TNT at $5 a stick. Need more" on the back of a business card.

10) The blast created a 30ft-wide, 8ft-deep crater on the street outside the Alfred Murrah Federal Building.

11) McVeigh was a gun fanatic and was taught to shoot by his grandfather. He told people he wanted to be a gun shop owner and sometimes took firearms to school to impress his classmates.

12) McVeigh was reprimanded by the military for purchasing a "White Power" T-shirt at a Ku Klux Klan protest against black servicemen who wore "Black Power" T-shirts around the army base.

13) In the aftermath of the bombing, The Salvation Army served over 100,000 meals and provided over 100,000 ponchos, gloves, hard hats and knee pads to rescue workers.

A family member of a victim observes silence at the Field of Empty Chairs memorialReuters

14) The national humanitarian response was overwhelming and caused logistical problems. Large numbers of items such as wheelbarrows, bottled water, knee pads and clothing were donated.

15) Some of the debris was used as evidence in the conspirators' trials, as well as incorporated into memorials, donated to local schools, or sold to raise funds for relief efforts.

16) In the days following the blast, over 12,000 people participated in relief and rescue operations.

18) Both McVeigh and Nichols had expressed anger at both the FBI's 1992 stand off with Randy Weaver at Ruby Ridge, as well as the federal government's handling of the 1993 Waco siege, both of which inspired their attack in Oklahoma.

19) During the attack, McVeigh carried pages from The Turner Diaries, a 1978 novel by William Luther Pierce in which supremacists who start a violent revolution to exterminate the US federal government.

20) McVeigh's execution in 2001 was the first federal execution in 38 years.